I find that single bunnies tend to sit around more and move a lot less. Bunnies in pairs or more enjoy chasing and playing and do cover a lot more ground as they are doing what they are supposed to do. I think single bunnies lack the motivation of a friend to actually get up and run about more - although that is not an excuse to keep them in an inadequate space, more an incentive to make 2 or 3 bunnies happier with each other.

I prefer my two to have 'areas', separated by tubes, so they can go and grump off and be moany with each other when they want, and go back and be forgiven when they want. Neither has claimed an area as their own (though they'll chin everything in reach of course, but no fighting over it), and putting them into their big area on the lawn has never instigated anything that hasn't happened everywhere else anyway.